For most used-car buyers it would be a dream come true: Your car actually gains in value, instead of depreciating.

When Kelley Blue Book looked at depreciation of used cars from May 24 to the same day last year, it found 23 examples of used cars that had gained in value during that time. Among them:

A 2012 Chevrolet Malibu was valued at an average $13,450, up 4.1% from $12,925.

A 2009 Kia Sorento averaged $11,975, up 4.8% from $11,425.

A 2012 Subaru Forester came in at $17,350, a 5.8% boost from $16,400. The 2011 model was up, as well.

One key factor in the favor: All would have been bought as used cars, missing the first year or more of depreciation that is often the steepest.

"It does happen from time to time," says KBB analyst Alec Gutierrez. "In any given calendar year, there are times when used-car values are appreciating."

Usually, it's a matter of timing. Used-car prices at wholesale are often weak during the winter when icy roads and wet weather dissuade auto dealers from stocking up. In the spring, more go to the wholesale auctions, and prices are bid up. The effect was more pronounced this year because of the long, hard winter, he says.

Overall, though, prices of cars usually fall. Only when you get "flukey circumstances" can they rise," says Tom Kontos, economist for Adesa, one of the major wholesale auction houses.

He recalled how prices of used fuel-thirsty SUVs fell deeply during the gas price run-up of 2008, only to rebound when gas prices fell.

"Most cars depreciate," he says, and lately the trend has been for even softer prices.

When CarGurus.com, an auto buying research website, studied used-car value trends, it found those that were best at retaining value — including some that gained value — were generally pickup trucks. The biggest losers when it came to depreciation were luxury cars.

Pickups "really hold their value," says Langley Steinert, CarGurus.com's CEO. "These are utilitarian. They are not going to be loaded up with options," which used car buyers don't value.